1. Field of the Invention
The invention is in the field of the automatic processing of flat objects such as letters.
More particularly, the invention relates to a buffer system for carrying out a buffer process comprising the feeding of flat objects, such as letters, provided with scannable symbols, in an unordered sequence, temporarily storing them and discharging them in an ordered sequence and to a buffer as storage medium in such a buffer system. An unordered and an ordered sequence is understood to mean a sequence in no way determined, and in some way determined, in or by the system. The buffer process serves the processing mentioned which may comprise, for example, a video coding process or a sorting process. The invention is therefore also directed at a video coding device and a sorting device in which such a buffer system is used.
2. Prior Art
The use of postal codes on letters in principle permits an increasingly more rapid and more precise automatic postal processing. All this is achieved by carrying out the processes such as, for example, the sorting by analogy with the treatment of data in a computer. However, such a treatment requires that throughout the entire duration of the actual processing of a number of letters which is preferably large in a sorting process, in particular the position of every letter is and remains precisely known in a control system, under the control of which the processing and the conveyance for the purpose thereof takes place. This requires a temporary storage medium with great flexibility, that is to say that every letter must be capable of being stored individually and selectively therein and then ejected at time instants which are precisely determined by the control system for the purpose of the process and on the basis of instantaneously determined selection criteria. By analogy with a (memory) buffer for the temporary storage of a character or word in a computer, such a storage medium is called a buffer or buffer system, it being possible for a buffer system to encompass more than one buffer.
Buffer is therefore understood hereinafter to mean a storage means for the temporary individual storage of objects fed along a feed track, which storage means comprises a number of buffer pockets each capable of accommodating, under the control of control means, an object from the feed track, retaining it temporarily and ejecting it in the direction of a discharge track.
German Auslegeschrift 1,277,606 discloses a letter sorting device for sorting letters at a delivery point, the letters being provided with a sorting code. This device comprises a number of storage means, sited in rows, each of the type of an intermediate stacker. Each intermediate stacker is provided at its inlet with a stacker and at its outlet with a destacker. The inlets of said intermediate stackers are connected to a feed conveyance track with branches starting from an inlet, while the outlets thereof are connected to branches, converging again into one track, of a discharge conveyance track. The feed and discharge conveyance over a row of intermediate stackers is of the driving/entraining conveyance type achieved by clamping the letters between a driven, laterally elastic, endless conveyor, and sliding surfaces sited respectively between successive inlets and outlets of the intermediate stackers. A predetermined sorting code corresponds to each intermediate stacker. Arranged near the inlet of the feed conveyance track is a sorting code reader for reading the sorting code displayed on the letters. Every letter having a particular sorting code is then passed to the intermediate stacker corresponding to that sorting code. On a signal delivered from an operating console, an intermediate stacker corresponding thereto is able to destack itself, whereupon the letters are passed in a sequence in which they were stacked in the intermediate stacker over the discharge conveyance track to the outlet of the device in order, if necessary, to be discharged as bundles at that point. A sorting device related thereto is disclosed by the U.S. Pat. No. 4,388,994. In addition to a first sorting code reader along an input track and first storage means comprising a number of intermediate stackers connected to the input track and having a common ejection conveyance track, this device also comprises second storage means formed by a row of storage locations each capable of temporarily storing a letter individually. After a first sorting in the intermediate stackers, the letters are ejected repeatedly for each intermediate stacker and fed past a second sorting code reader in the common ejection conveyance track and then, under the control of the control means, temporarily stored in a desired sequence in the row of storage locations. Finally, the letters are simultaneously released in said sequence from said storage locations for ejection along a common discharge track to the outlet of the device. For the purpose of the simultaneous ejection, the storage locations have a width which has to be greater than the maximum permitted letter length. At the inlet side of a row of storage locations, a first, single endless conveyor forming a feed track runs over the entire length. Each storage location is formed by two interacting endless conveyor belts, of which one preceding the entrance of the storage location and also running in parallel over a certain length always interacts with the endless conveyor for the purpose of conveyance in the storage location. The said endless conveyor belts separate over a certain distance (at least equal to the maximum letter length), which produces a storage space for a letter. At the end of said space there is a stop handle which can assume two positions, one in which a letter is retained, (the letter then remains in slipping contact with one of the conveyor belts,) and one in which the letter is released for further conveyance to the outlet side of the storage location by the two endless conveyor belts, which are again interacting, past the stop handle. The conveyance at the outlet side takes place in a similar way to that at the inlet side. Opposite every inlet of a storage location there are, at the other side of the conveyor, gate means which, at a command (of a control signal) can intervene in the feed track in order to route a certain letter to the storage location corresponding to the gate means. This known technique suggests as gate means those of the roller type with which the first endless conveyor is pushed in the direction of the inlet at the position of the first endless conveyor. A row of storage locations related to the second storage means from the US Patent Specification cited is disclosed by German Patent Specification No. 2,945,386. This patent specification describes a video coding system for applying a code to letters fed to the system corresponding to their address data presented on video screens. Such a code can only be applied to the letters at the outlet from the system after address data have been presented on a video terminal and a corresponding address code has then been fed to the system by human intervention. The time taken up, in particular, by said human intervention is very variable. Such a system therefore comprises a waiting section which, in said known technique, is composed of a combination of a relatively long loop in a first conveyance section and a row of storage locations for individual letters connecting thereto. If the address code of a letter which reaches the end of the loop has been fed to the system in the meantime, the letter is conveyed further in a second conveyance section in which printing means have been incorporated for printing a code corresponding to the address code supplied on the respective letter. However, if the address code has not yet been fed to the system at that time, the respective letter is fed to the row of storage locations and is stored in a free storage location having a priority assigned by the system which is highest at that instant until the address code is received by the system. A stored letter is ejected into the second conveyance section accurately harmonized in terms of time with interruptions in the flow of letters. Said interruptions occur either at the instant that a subsequent letter has to be stored or as a consequence of the temporary hold-up of the stream of letters at the beginning of the first transport section after a corresponding signal from the control system. The feed track and discharge track of this known row of storage locations are realized in a similar way to those in the technique cited above with the US Patent Specification. The actual storage location is bounded laterally by two guides sited in parallel, while the base of the storage location is formed by a permanently driven endless conveyor. Through the face of one of the guides there projects a permanently driven roller. At the inlet side, the space between the guides is openly accessible, while at the outlet side it can be shut off by a sort of barrier which is provided at the end of one arm of a two-arm lever. Mounted on the end of the other arm of the lever is a rotatable roller. The lever is rotatably mounted between two arms on a driveable shaft, as a result of which the lever can be set in two positions, one in which the barrier is closed and one in which it is opened and in which the rotatable roller and the driven roller can interact so as to convey. With the barrier closed, a letter in the buffer pocket is held upright between the guides and continuously pressed against the barrier by its own weight while making slipping contact with the permanently driven endless belt and roller. If the barrier is opened by rotating the lever, conveyance is carried out by the base conveyor and the two interacting rollers in the direction of the discharge track. Opposite every inlet there are, at the other side of the endless conveyor which determines the feed track, gate means of the roller type which, at a command (of a control signal), can intervene in the feed track in order to route a certain letter to the storage location corresponding to the gate means.
The storage techniques as known from the patent publications cited above have the following drawbacks. As used, in particular, in sorting devices, they lack the high degree of flexibility indicated above. Since, according to these storage techniques, letters are released at least once completely or virtually completely, the position of a letter is not always known equally precisely in the control system. Used for the individual storage of letters, these known techniques are unsuitable for relatively high processing speeds as a result of inadequate control of the object conveyance in the storage locations themselves; there is a relatively large occupation of space per storage location; owing to the continuous slipping contact of a stored letter with the conveyor, the storage duration can only be very limited since there is otherwise the risk that the letter becomes damaged; such a slipping contact with the bottom edge of the letter as known from the said German Offenlegungschrift may, in addition, soon lead to scores in the conveyor. The video coding system known from said Offenlegungschrift moreover also has the drawbacks that the ejection does not take place independently of the input and that during storage, the letters are not uniformly distributed over the storage locations with the result that a slanting wear may occur.